Universal long stroke pump system

ABSTRACT

The long-stroke pumping apparatus has a frame, a drum, and a pair of sheaves mounted on the frame. A traction cable is carried by the drum. A cable connector is connected to one end of the traction cable which is guided over one sheave into an oil well. A counterweight assembly is connected to the other end of the traction cable which is guided over the other sheave into a counterweight well. A reversible power means, preferably a hydraulic motor, rotates the drum a number of turns in one angular direction and then in an opposite direction during one complete stroke of pumping operation. A load cable is also supported and guided by the sheaves, and the cable connector and the counterweight assembly are also suspended from the opposite ends of the load cable. The load cable is not drivingly connected to the drum.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

This invention generally relates to a long stroke pumping apparatus foroil wells and the like and more particularly to a multi-cable universallong stroke pumping apparatus.

(b) Description of the Prior Art

A beam-type pumper is generally limited to a stroke length of about 16to 18 feet. The string of sucker rods accelerate from the start of eachstroke to the middle and decelerate from there to the end of the stroke.It was long recognized that a longer stroke and a slower but constantspeed for the sucker rods would be an improvement. Efforts havetherefore been made to build long-stroke pumpers. For example, U.S. Pat.Nos. 3,285,081 and 3,528,305 describe one such pumper.

Another long-stroke pumper is described in the November, 1976 issue ofWorld Oil, Pages 64-68. It is cable-operated by anelectronically-controlled electric motor. It utilizes a drum on which afirst cable is wound in one direction to raise and lower the rod string.A second cable also connected to the drum is pulled in the oppositedirection by a counterweight which partially balances the torque loadrequired to lift the rod string and the production fluid from the well.The steel wire cables wound on the drum have a large diameter andrequire large diameter sheaves. The drum itself is rotated by ahigh-torque gear box driven by the electric motor which is mechanicallyswitched to operate in forward and reverse for up and down strokes. Thedrum's surface is provided with spiraling grooves, or cams, which causethe cables to follow paths that change the radius of the drum near theend of each stroke, thereby altering respective torque loads on thewell-side and on the counterweight-side cables. As a result, thecounterweight-torque is decreased by a smaller radius and the upwardmotion will stop and reverse. Similarly, at the bottom of the stroke,the well-side torque is decreased by a smaller radius and the downwardmotion will stop and reverse. During a portion of this pendulum typemotion, the electric motor is switched off, otherwise it is required tosupply power over most of the length of each stroke. The direction ofrotation of the motor is controlled by conventional mechanical reversingcontactors that are actuated by an electronic system. At the proper timeduring each stroke, the motor is switched off or on as required.

The great number of such required on-and-off switching operationsproduce wear and tear. The stroke length and the number of strokes canbe adjusted but over a relatively limited range of about ±10%.

While the prior art cable-operated long stroke pumpers constitute animprovement over the conventional beam-type pumpers, nevertheless theyare still characterized by drawbacks chief among which are: they requirelarge diameter drums, sheaves and cables; their cables become subjectedto excessive wear; their electric prime movers require high torque gearboxes to rotate their drums and no other type prime movers can beemployed; their physical dimensions and weights, while reduced ascompared to the beam type pumpers, are still excessively large to makefull enclosures practical, hence excessive wear on the pumper units;they are inherently restricted to the limited operational range they aredesigned for; their velocity and acceleration are not easilyprogrammable; they are insensitive to downhole problems and willcontinue to work until a sensed overload will set an electronic brake,or until a catastrophic failure occurs; and should their single cablebreak on the wellside, the rods which will accelerate downwardly willbuckle, the downhole pump will most likely become destroyed, and theproduction tubing damaged.

It is therefore a general object of the present invention to provide auniversal long-stroke pumper (ULSP) which retains the advantages ofprior art long-stroke pumpers while eliminating their above describedand other known disadvantages.

SUMMARY OF THE INVENTION

The long-stroke pumping apparatus has a frame, a drum, and a pair ofsheaves mounted on the frame. A traction cable is connected to the drum.A cable connector is connected to one end of the traction cable which isguided over one sheave into an oil well. A counterweight assembly isconnected to the other end of the traction cable which is guided overthe other sheave into a counterweight well. A reversible power means,preferably including a hydraulic motor, rotates the drum a number ofturns in one angular direction and then in an opposite angular directionduring one complete stroke of pumping operation. A load cable issupported and guided by the sheaves, and the cable connector and thecounterweight assembly are also suspended from the load cable. The loadcable is not drivingly connected to the drum.

Preferably, the pumping apparatus includes a plurality of load cablesand at least two traction cables. The reversible power means is poweredby a hydraulic system having a hydraulic control network and ahydrostatic transmission which includes a prime mover, avariable-delivery hydraulic pump driven by the prime mover, and thereversible hydraulic motor is powered by the pump. The hydraulic motoris preferably directly coupled to the drum. The hydraulic motorpreferably has a stator shaft and a rotor directly coupled to the drum.The hydraulic control network includes means for independentlycontrolling the rate of hydraulic power delivered by the pump to themotor during each up-stroke and down-stroke.

The pumping apparatus preferably further includes means for displacingthe drum relative to the sheaves simultaneously with and in relation tothe rotation of the drum by the hydraulic motor. The rate of suchdisplacement of the drum is adjusted to produce a substantially zerofleet angle for the traction cable or cables during the entire cycle ofpumping operation. The displacement of the drum is produced preferablyby pivoting the drum, which can be achieved by mounting the drum on asupport which is pivotably mounted on said frame. The hydraulic controlnetwork includes a servo loop for controlling the rotation of the drumand for pivoting the drum support in response to an error signalproduced by a sensor device which senses the lateral position of atraction cable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the overall ULSP showing the surfaceunit, the counterweight well, and the top section of the productionwell;

FIG. 2 is an enlarged perspective view of the surface unit shown in FIG.1;

FIGS. 3-8 are schematic illustrations of different cable arrangementssuspended from the drum and sheaves useful for an understanding ofcertain theoretical considerations of the ULSP;

FIG. 9A is a side view of the drum and its movable platform;

FIG. 9B shows the alignment between the traction cables and theirrespective grooves on the sheaves when the drum's axis is horizontal;

FIG. 9C shows the same alignment when the drum's axis is maximallytilted upwardly relative to the horizontal;

FIG. 10 is a schematic and exploded view of the hydrostatic transmissionand of hydraulic control network;

FIG. 11 shows a conventional wellhead for sucker rod pumping;

FIG. 12 is a sectional view of the bottom part of the modifiedproduction well used with the ULSP of this invention;

FIG. 13 is a view on line 13--13 in FIG. 12; and

FIG. 14 shows the upper part of the modified production well.

DETAILED DESCRIPTION OF THE ULSP

Throughout the drawings and to facilitate their understanding, the samereference characters will be used to refer to the same or similar parts.The description of conventional parts will not be given except whenrequired for an understanding of the modifications brought about by thepresent invention.

The universal long-stroke pumper (ULSP) of this invention is generallydesignated as 10 (FIG. 1). It comprises a surface unit 12, acounterweight well 14, and a modified oil production well assembly 16.The surface unit 12 is disposed on the ground so that its front end isadjacent to well 16 and its rear end is adjacent to well 14. Unit 12 hasa main frame 13 on which are mounted rear and front cable guides,preferably a rear sheave 18 and a front sheave 19, each sheave beingrotatably mounted about a horizontal axis, the axis of sheave 18 beingparallel to the axis of sheave 19. The circumferential surface of eachsheave has a number of parallel grooves corresponding to the totalnumber of cables employed. The greater the number of cables, the smallercan be the diameter of each cable and consequently the smaller can bethe diameter of each sheave. Sheave 18 guides the set of cables 20 intothe center of well 14. Sheave 19 guides a set of cables 21 into thecenter of well 16. The ends of cables 20 are attached in any convenientmanner to a counterweight assembly 22 which can be made up of aplurality of discs 22'. The counterweight assembly 22 is guided on camrollers 24 over diametrically-disposed, vertical rails or guides 26which are welded to the pipe 23 forming well 14. In this fashion, well14 need not be vertical with great accuracy. The guided counterweight 22thus prevents the rotary motion of and twisting of the set of cables 20.

On the frame 13 (FIG. 2) of surface unit 12 is mounted a prime mover,which can be a diesel engine or an electric motor 32. An electriccontroller 35 controls the operation of motor 32. A hydraulic system 30is provided which consists of a hydrostatic transmission 30a and of ahydraulic control network 37. Motor 32 has a shaft 33 directly coupledto the shaft of the hydrostatic transmission 30a which includes avariable-delivery pump 34. Pump 34 provides variable and reversiblehydraulic power to a reversible hydraulic motor 36.

The hydraulic control network 37 derives fluid from and rests on ahydraulic tank 38. Network 37 controls the entire operation of the ULSP10. A heat exchanger 39 driven by a small hydraulic motor 41 removesheat from the hydraulic fluid in system 30. Motor 36 is of a type whichcan preferably be mounted in the center of, for driving directly, a drum40 having a helical groove on its circumferential surface. To avoidexcessive wear on the cables, drum 40 is rotatably mounted on a drumsupport 42. The drum's surface is controllably movable so that the fleetangle is substantially zero at all times. This can be accomplished forexample by reversibly rotating the drum support 42 by a small angleabout a horizontal axis perpendicular to the axis of the sheaves andpassing through the center of the drum, at the same time as drum 40rotates clockwise or counterclockwise. The same object can beaccomplished by reversibly moving the drum support horizontally on aline parallel to the axis of the drum, or by any other means reversiblymoving or displacing the drum in a line parallel to the drum's axis,although it is presently preferred to pivotably mount the drum support,as shown in the drawings.

Before proceeding with the further description of the ULSP 10, it willbe helpful to first describe certain theoretical aspects of theinvention with reference to FIGS. 3-8. FIG. 3 illustrates a single cable51 guided over sheaves 18 and 19. Attached to the rear end of cable 51is counterweight 22 having a weight Ci. Attached to the front end ofcable 51 is a sucker rod string 110 which is conventionally representedby a weight Wr that carries, on the upstroke only, a fluid weight Wf.The counterweight 22 is selected so as to satisfy the followingrelationship:

    Ci=Wr+Wf/2                                                 (1)

Equation 1 for the sake of simplicity does not take into considerationfriction, buoyancy of the sucker rod string 110, and other factors ofsecondary importance.

Cable 51 will hereinafter be referred to as a "load" cable todistinguish it from a traction cable, generally designated as 54 (FIG.4). The load cable 51 is not drivingly connected to the drum 40.Traction cable 54 consists of a half-traction cable 54a on thecounterweight side and of a half-traction cable 54b on the sucker rodside. The helically grooved surface of drum 40 has n turns between twoend points 40a and 40b (FIG. 5). Half-traction cable 54a has one endanchored at 40a and its other end attached to counterweight 22.Half-traction cable 54b has one end anchored at 40b and the other endattached to the rod string 110. Cables 54a and 54b always exit from drum40 from two adjacent grooves. When drum 40 is fully rotated clockwise,cable 54b is fully wound up and cable 54a is fully unwound, and viceversa.

It is desired for the load cable 51 and the traction cable 54 to be ofequal strength and of the same diameter. The load and traction cables 51and 54 will carry the same loads provided that the followingrelationship is satisfied:

    Wf≦2 Wr                                             (2)

FIG. 6 illustrates the case wherein two load cables 51, 52 and onetraction cable 54 are employed. In order for all the cables to share theloads equally, the following relationship must be satisfied:

    Wf/2≦Wr/2                                           (3)

For small to medium size loads, the utilization of two load cables andone traction cable will be sufficient. For large size loads, it will beconvenient to employ three load cables 51, 52, 53 and two tractioncables 54, 55 (FIG. 7). To accommodate two such traction cables, thedrum surface is provided with a double helical groove in which the twotraction cables are wound side by side (FIG. 8). Half-traction cables54a, 55a are anchored to adjacent end points 40a, 40a', respectively, atone end of the drum and half-traction cables 54b, 55b are anchored toadjacent end points 40b, 40b', respectively, at the opposite end of thedrum.

In order for the five cables 51-55 to share the loads equally, thefollowing relationship must be satisfied:

    1/2Wf/2≦Wr/3 or Wf≦4/3 Wr                    (4)

In general, in the case wherein n traction cables and m load cables areemployed, the loads will be shared equally by all the cables providedthat the following relationship is maintained:

    Wf≦2n/m Wr                                          (5)

In sum, while the load cables are not essential, they are highlydesirable since they serve to separate the traction effort from thestatic load, thereby leaving to the traction cables the job of providingthe necessary pull for the fluid production load Wf.

When the drum's longitudinal axis is horizontal (FIG. 9), then the exitpoint 54a' (FIG. 9B) of the half-traction cable 54a from the drum willbe in alignment with its corresponding groove on sheave 18, and the exitpoint 54b' of the half-traction cable 54 will be in alignment with itscorresponding groove on sheave 19. The exit points 54a' and 54b' areadjacent to each other near the center of the drum's surface.

In order for the fleet angles of the two half-traction cables to be atall times substantially zero, i.e., in order for each half-tractioncable to continuously remain in alignment with the groove on the sheave,the drum's support 42 is made to pivot about an axis passing through thecenters of stub shafts 42a, 42b (FIG. 9A). Stub shaft 42a is journaledin a pair of thrust bearings 42c and in a load bearing 42d. Stub shaft42b is journaled in a load bearing 42e. The angular rotation of stubshafts 42a, 42b to which the support 42 is secured will determine theangle of tilt imparted to the longitudinal axis of the drum. The greaterthe number of turns of the traction cable on the drum's surface, thegreater will this angle of tilt have to be.

When the drum is fully rotated clockwise, as viewed in FIG. 9C, cable54b is fully wound and cable 54a is fully unwound, so that theirrespective exit points 54b', 54a' will be at one end of the drum. Thedrum's support 42 is then fully tilted counter-clockwise so that exitpoints 54a', 54b' again remain in alignment with their grooves onsheaves 18, 19. Conversely, when the exit points 54a', 54b' are at theopposite end of the drum, the support 42 is then fully tilted clockwise,so that exit points 54a', 54b' again remain in alignment with theircorresponding grooves on sheaves 18, 19.

Thus during a full cycle of pumping operation, i.e., a complete up anddown stroke, support 42 first gradually tilts counter-clockwise and thenclockwise. The oscillations of support 42 achieve a very importantfunction which consists of substantially removing the lateral frictionwhich would otherwise exist in the half-traction cables. Although thetension itself within the half-traction cables would be sufficient totilt support 42 in order to maintain the exit points 54a', 54b' inalignment with their respective grooves on their respective sheaves, inorder to remove all side-loads it is preferred to apply an assist torqueto the stub shaft 42b, as will subsequently be described. Thus while thedrum rotates about its longitudinal axis to provide a long stroke, thedrum's longitudinal axis is tilted so that the exit points of thehalf-traction cables remain lines up with the grooves on theirrespective sheaves.

The hydraulic system 30 (FIG. 2) will now be described in greater detail(FIG. 10). The hydrostatic transmission 30a includes the electric motor32 whose shaft 33 is coupled to the variable-delivery hydraulic pump 34that delivers hydraulic power through a pair of flexible, high-pressurelines 61, 62 to the stationary shaft or stator 36a of the hydraulicmotor 36. Although any high-torque, low-speed hydraulic motor can beemployed, a Hagglunds series 40 motor, sold by the Bird-Johnson Company,is preferred. Its rotor 36b is secured to drum 40. The stator 36a isstationary on frame 42. For clockwise rotation of rotor 36b,high-pressure oil flows into line 61 and returns through line 62.Conversely, for counterclockwise rotation, high-pressure oil flow intoline 62 and returns through line 61. The front section of the main pump34 contains an auxiliary charge pump 34a and a servo control 34b whichcontrols the delivery of the main pump 34. A rotatable shaft 63 extendsoutwardly from the servo control 34b and its free end is connected to anL-shaped control link 64, one leg 64a of which is connected to the rod65 of a hydraulic cylinder 66, and its other leg 64b carries a pin 72.Rod 65 carries a disc 67 which is movable between two stop members suchas threaded bolts 68, 69. Shaft 63 extends through the base of link 64into the leg 70b of an override link 70 having a Y-guide. Pin 72 ridesinside the head section 70a of the Y-guide, as shown. The override link70 is secured to the rod 71 of a hydraulic cylinder 73.

The charge pump 34a supplies fluid to the hydraulic control system 37through line 74 which feeds: a pair of spring-loaded, four-way controlvalves 75, 76; a pressure regulator 77; and a flow regulator 78. Theoutput from regulator 78 is fed through a line 79 to a pair ofspring-loaded four-way control valves 80, 81, and to a relief valve 82whose output is returned through a drain line 83 to the oil tank 38. Theoutput from oil tank 38 flows through a filter 84 into the charge pump34a, and the excess oil is returned to the tank through a line 85.

Valve 76 has a shaft 76a which is mechanically coupled to a plate 86that carries two spaced-apart cam rollers 81a, 81b between which passesthe traction cable 54b connected to the sucker rod 110. Secured to thefree end of an extension 46b' of shaft 42b is a cam plate 88 thatoperates valves 75, 80, and 81. Plate 88 has a bottom arcuate sectionwhich carries two adjustably positioned cams 88a, 88b that operate theshafts of valves 80, 81, respectively. Cams 88a and 88b are normallypositioned next to each other near the center of the arcuate section ofplate 88 (FIG. 10), and then the maximum number of traction cable turnswill be wrapped and unwrapped on and from drum 40. When cam 88a is movedto the left of center, the number of turns that cable 54a will wraparoung the drum will be reduced and cable 54b will equally unwrap alesser number of turns. The reverse happens when cam 88b is moved to theright of center. The particular position of either cam 88a or 88b isdetermined by the operator prior to starting the pumping operation.

Valve 75 is actuated by lobes 88c and 88d on the opposite sides of thetop end of cam plate 88. Valve 75 controls an electric switch 75a whichis a fail-safe device that functions only in the vent that the controlprovided by valves 80, 81 fails. Valve 75 will be actuated by lobe 88cor 88d before the half-traction cable 54a or 54b reaches the end of thedrum.

The extension shaft 46b ' also carries a lever arm 89, the outer end ofwhich is pivotally connected to the rod 90 of a hydraulic cylinder 91.The output from valve 80 is fed through a line 92 to one inlet ofhydraulic cylinder 66. The outlet of valve 81 is coupled through a line93 to the other inlet of cylinder 66. The output of valve 75 is coupledthrough a line 94 to one inlet of hydraulic cylinder 73. Outlets 76b,76c of valve 76 are connected through lines 95, 96, respectively, to thetwo inlets of hydraulic cylinder 91.

In operation of the hydraulic system 30, when shaft 63 is at its neutralor center position, no oil is flowing in either line 61 or line 62, eventhough pump 34 is being rotated at full speed by shaft 33 of electricmotor 32. When shaft 63 is rotated counterclockwise to its extremeposition, by an angle of say 28°, as viewed in FIG. 10, oil will flowinto hydraulic motor 36 through line 62 and will return to pump 34through line 61. Rotor 36b and therefore drum 40 will rotate at fullspeed in a counter-clockwise direction. Conversely, when shaft 63 isrotated clockwise from its center position to its extreme position, oilwill flow into line 61 and will return through line 62. Rotor 36b anddrum 40 will rotate at full speed in a clockwise direction. The angularspeed of rotor 36b will depend on the angular deviation of shaft 63 fromits center position, because the volume of oil delivered by pump 34 isproportional to the angular deviation of shaft 63 from its centerposition.

The angular rotation of shaft 63 is produced by the up and downmovements of rod 65 which are translated into rotary motion by link 64.Since the movements of rod 65 are limited by the stop members 68, 69,the rotation of shaft 63 in either direction will also be limited by thesame stop members. As a result, stop member 69 will limit the maximumcounter-clockwise speed of drum 40, and stop member 68 will limit themaximum speed in a clockwise direction.

In the event of an emergency, rod 71 will contract, thereby confiningpin 72 within the leg 70b of the Y-guide in the override link 70. Suchaction has the effect of returning shaft 63 to its neutral or centerposition, so that no fluid will flow in either line 61 or line 62,thereby stopping drum 40.

The cam rollers 81a, 81b sense the lateral movements of half-tractioncable 54b. When cable 54b is in alignment with its corresponding grooveon sheave 19, then shaft 76a of valve 76 will be in its neutral positionand no oil will flow through lines 95, 96. Should the half-tractioncable 54 become laterally displaced from its alignment position by apredetermined amount, on either side from the neutral position, theneither cam 81a or cam 81b will transfer a force or "error" signalthrough plate 86 to shaft 76a of valve 76 in a direction correspondingto the direction of the displacement of cable 54b. The movements ofshaft 76a will cause oil to flow in either line 95 or line 96, therebycausing either an extension or contraction of rod 90. The linearmovements of rod 90 are translated into angular rotation of lever 89 andtherefore of shaft 42b. The rotation of shaft 42b will produce acorresponding rotation of the drum's support 42 and, hence, a tilt ofthe longitudinal axis of drum 40 in a vertical plane about the center ofthe drum. The rotation of support 42 and hence the angle of tilt of thedrum's longitudinal axis will be in a direction so as to remove thelateral displacement of cable 54b and bring it back into alignment withthe groove on sheave 19. In this manner the fleet angle will besubstantially zero at all times.

The charge pump 34a will supply oil through line 74, at a pressure ofsay 200 psi, to valves 75, 76 and to a pressure regulator 77 adjusted toabout 25 psi. The output of regulator 77 is fed through a flow valve 78which can be regulated from 100 to 400 cubic inches per minute. Theregulated outflow of oil from regulator 78 flows through line 79 intovalves 80, 81 whose shafts are movable by cams 88a and 88b,respectively. The positions of cams 88a, 88b will be manually adjusteddepending on the number of drum revolutions desired during each halfcycle of pumping operation, and hence on the length of each desiredup-stroke or down-stroke.

When valve 80 becomes actuated by cam 88a, oil will flow through line 92into cylinder 66 thereby causing its rod 65 to contract, which in turncauses link 64 and control shaft 63 to rotate clockwise. The rotation ofshaft 63 clockwise forces pump 34 to reduce its rate of oil deliverythrough line 62 to zero, and then to resume delivery through line 61 upto a maximum rate determined by the position of bolt 68. When valve 81becomes actuated by cam 88b, oil will flow through line 93 into cylinder66 thereby extending rod 65 and causing link 64 and control shaft 63 torotate counterclockwise. As a consequence, pump 34 will reduce its rateof delivery through line 61 to zero and resume delivery through line 62to a maximum rate determined by the position of bolt 69. Thus therotation of shaft 63 in a clockwise direction first reduces the speed ofdrum 40 in a counterclockwise direction to zero, and then reverses thedrum's rotation to a clockwise direction. Thus during each full cycle ofpumping operation, drum 40 will accelerate clockwise and then acceleratecounter-clockwise.

The transition from clockwise to counter-clockwise, rotation, and viceversa, is achieved smoothly and continuously at a rate determined by afluid flowing through flow valve 78. The adjustment of flow valve 78will determine the speed at which rod 65 of cylinder 66 can extend orcontract and, therefore the rate of acceleration and deceleration ofdrum 40. Hence, flow valve 78 provides a convenient means forcontrolling the acceleration and deceleration of the drum.

When valve 75 becomes actuated by cam 88c or 88d, it will allow oil toflow into cylinder 63 thereby causing rod 61 to contract, wherebyoverride link 70 moves up and link 64 is brought to its neutralposition, the results of which have previously been described. The powerexerted by cylinder 73 can overcome the resistance offered by cylinder66, because the pressure line 79 is returned to the drain line 83through a relief valve 82 set at 35 psi. When valve 75 becomes actuated,electric switch 75a will interrupt the flow of current to motor 32. There-energization of motor 32 can be effected manually after themalfunction has been repaired.

With reference to FIG. 11, a conventional well head, generallydesignated as 100, comprises a casing head 101 which supports concentriccasing strings 102, 103, and production tubing string 105 thatterminates above the well head in a T-pipe 106 that allows theproduction fluid to flow from the production tubing 105 into a pipeline.Casing head 101 is supported by the outer casing 104. Inside theproduction string 105 is positioned the polished sucker rod 110.

A stuffing box 112 mounted on rod 110 provides a seal fixed between theproduction string 105 and the polished rod 110. In this manner thepolished rod 110 can move up and down without any oil escaping where thepolished rod leaves the well head at point 111.

With reference now to FIGS. 12-14, the well head used with the ULSP 10of this invention is generally designated as 120. It comprises anenlarged diameter production string 122. To the bottom end of string 122is coupled a swaged nipple 124 which serves as a transition couplerbetween the large diameter string 122 and the reduced diameterproduction string 105. A short piece of production pipe 105 extends intothe lower end of the swage nipple 124 and is welded thereto at a point123. Pipe 105 is provided above point 123 with a plurality of radiallyspaced-apart orifices 126 which allow the production oil to dischargeinto a fluid reservoir chamber 127. Welded near the uppermost end of theproduction pipe 105 is an annular ring 130 which supports a tubularsection 131 that surrounds production pipe 105 and is sealed therefromby one or more O-rings 132. The upper end of section 131 is attached toa conically-shaped section 133 which then changes to a rectangularcross-section. The bottom end 134 of a rectangular cross-section. Thebottom end 134 of a rectangular cable guide 136 is welded to section133. An annular ring 129 supports seals 138 the movement of which isstopped by an upper ring 140.

The polished rod 110 extends through seals 138 and terminates in aclevis 142 which is attached to a cable connector plate 144, alsopreferably having a rectangular cross-section. Plate 144 is providedwith opposite cam rollers 146 which will permit the plate to move easilyinside the rectangular guide 136. The set 21 (FIG. 1) of cables from thesheave 19 are secured to plate 144 by any suitable means.

The well head 120 includes the outer casing 104, one or moreintermediate casings 102, the enlarged diameter production string 122,and the cable guide 136 which will protrude from the well head through atop plate 148. A discharge tube 150 connects the fluid reservoir chamber127 with the production pipeline.

In one embodiment of the invention, the frame was 12' long and 5' wide,the sheaves had a 33-inch diameter and carried five 3/4-inch cables sideby side, three of which were load cables and two were traction cables.For a well head using a 2-inch or 2.5-inch production string 105, theuppermost 45-foot section thereof was replaced with a 4.5 inch enlargeddiameter string 122. A 24-inch swage nipple acted as a transitioncoupler between the 4.5-inch and 2-inch production tubings 105. A short2-inch pipe 105 extended into the nipple a distance of about 15-inchesand was provided with six circumferentially- spaced ports. Therectangular cable guide section 136 guided the set 21 of cables withouttwisting them and without putting pressure on the seals of the stuffingbox which can be conventional, but self-adjusting hydraulic cylindertype seals are preferred. The drum was 11-inches wide and had a diameterof 32-inches. The drum's surface had two parallel helical grooves, eachgroove had 6.5 turns. For a 3/4 inch cable, the depth of the groove wasabout 0.35 inches. For a 40-foot stroke, 4.6 turns of the drum wererequired. As the counterweight appears heavier on a down-stroke (withoutfluid load) and ligher on the up-stroke (with fluid load), the sytemcannot freewheel. If the traction cables are removed the system willstop.

ADVANTAGES OF THE ULSP

The advantages of the ULSP can be summarized with reference to theexamplary dimensions above given as follows: its forty-foot long strokeproduces highly efficient pumping at one to five strokes per minute withlong rod life and low acceleration; its multi-load cables allow thesheaves and the drum to have relatively small diameters requiring lowerdrive torques that can be produced from a hydrostatic transmission witha variable delivery pump; its hydraulic control system can independentlyvary the speed, stroke and acceleration thereby having the capability ofadjusting the ULSP operation exactly to the required well's conditionsfor optimum efficiency of operation; its hydraulic control network alsopermits to tune the ULSP so as to provide lowest torque and equalworkloads in both up and down motion for maximum efficiency. The controlnetwork includes hydraulic safety devices which continuously sense wellproblems and are capable of shutting down the pumping operation wheneveran abnormality occurs, for example, an instanteous excessive overloadwill instantaneously open a hydraulic safety release valve which willshut down the operation of the ULSP; a single mechanical embodiment ofthe ULSP can be driven with different hydrostatic transmissions so thatthe single mechanical ULSP is universal and can replace virtually thewhole range of conventional beam-type pumpers; its physical dimensionscan be such that the required amount of steel is considerably reduced,say by a factor 5 to 8, as compared to conventional long-stroke pumpers;and therefore, its reduced physical dimensions now make it practical tocompletely enclose the ULSP thereby protecting it from adverseenvironmental effects and making it less objectionable to the aestheticappearance of the pumping site. Other advantages will become readilyapparent to those skilled in the oil well pumping art.

What is claimed is:
 1. In a long-stroke pumping apparatus comprising: a rotatable drum, a pair of rotatable sheaves, traction cable means drivingly connected to said drum for transmitting the torque produced by said drum, cable connector means connected to one end of said traction cable means which is guided over one sheave into an oil well, a counterweight assembly connected to the other end of said traction cable means which is guided over the other sheave into a counterweight well, reversible power means for rotating said drum a number of turns in one angular direction and then in an opposite angular direction during one long cycle of pumping operation; the improvement wherein said reversible power means includes a hydraulic system having a hydraulic control network and a hydrostatic transmission, said transmission including: a prime mover, a variable-delivery hydraulic pump driven by said prime mover, and a reversible hydraulic motor powered by said pump and being directly coupled to said drum; and load cable means coupled to said cable connector means through said one sheave and to said counterweight assembly through said other sheave, said load cable means being drivingly unconnected to said drum.
 2. The pump apparatus of claim 1, wherein said hydraulic motor has a stator shaft and a rotor which is directly coupled to said drum.
 3. The pump apparatus of claim 1, wherein said control apparatus includes means for independently controlling the rate of hydraulic power delivered by said pump to said motor during each half cycle of pumping operation.
 4. The pump apparatus 3, and means for moving said drum relative to said pair of sheaves simultaneously with and in relation to the rotation of said drum by said hydraulic motor.
 5. A universal long-stroke pumping apparatus comprising:a frame, a drum support rotatably mounted on said frame, a helically grooved drum rotatably moun:er on said drum support, a rear multi-grooved sheave mounted for rotation about a horizontal axis on said frame on the side of a counterweight well, a front multi-grooved sheave rotatably mounted on said frame on the side of an oil well, at least one load cable supported on and guided by said sheaves into said counterweight well and into said oil well, traction cable means connected to and extending from said drum over said rear sheave into said counterweight well and over said front sheave into said oil well, a hydraulic system including: a hydrostatic transmission having a hydraulic motor directly coupled to said drum, and a variable-delivery pump hydraulically coupled to said motor; a primer mover for driving said hydrostatic transmission, and a hydraulic control network causing said hydraulic motor to rotate clockwise during one-half cycle and counter-clockwise during the other half-cycle of pumping operation, whereby said traction cable means effectuate in their respective wells a long stroke, a sensing device for producing an error signal dependent upon the lateral movements of said traction cable means, and said control network being responsive to said error signal for moving said drum support in a direction so as to reduce said error signal.
 6. A universal long stroke pumping apparatus for oil well pumping and the like comprised of:(i) a reversible power means, (ii) a rotatable grooved drum operatively connected to be periodically rotated by said power means during a pumping cycle of said apparatus, (iii) a pair of spaced-apart cable guide means, (iv) traction cable means being drivingly coupled to said drum for operatively connecting said drum through said guide means to a pumping string and to counterweight which at least partially counterbalances the weight of the pumping string, the improvement including: load cable means for carrying the loads of said pumping string and of said counterweight, said load cable means being drivingly unconnected to said drum.
 7. The pumping apparatus of claim 6, wherein said load cable means are supported on and guided by said cable guide means.
 8. The pumping apparatus of claim 7, wherein said traction cable means includes at least two traction cables.
 9. The pumping apparatus of claim 7, wherein said reversible power means includes a control network, a prime mover, a variable-delivery hydraulic pump driven by said prime mover, a reversible hydraulic motor powered by said pump, and said drum being driven by said reversible hydraulic motor.
 10. The pumping apparatus of claim 9, wherein said hydraulic motor is directly coupled to said drum.
 11. The pumping apparatus of claim 9, wherein said hydraulic motor has a stator shaft and a rotor, and said rotor is directly coupled to said drum.
 12. The pumping apparatus of claim 11, wherein said variable-delivery pump includes means for controlling the rate of hydraulic power delivered by said pump to said motor.
 13. The pumping apparatus of claim 9, and moving means for displacing said drum relative to said pair of cable guide means while said drum is being rotated by said reversible power means.
 14. The pumping apparatus of claim 13, wherein said moving means cause said traction cable means to maintain a substantially zero fleet angle during the pumping cycle.
 15. The pumping apparatus of claim 13, wherein said moving means pivot said drum about an axis which is substantially perpendicular to the axis of said drum and in substantially the same plane which contains the drum axis.
 16. The pumping apparatus of claim 13, wherein said moving means include a drum support which is pivotally mounted about a shaft whose axis is perpendicular to the axis of said drum.
 17. The pumping apparatus of claim 16, wherein said control system includes servo loop means for controlling the rotation of said drum and the pivoting of said drum support.
 18. The pumping apparatus of claim 17, wherein said servo loop means include sensor means for sensing the lateral position of said traction cable means on said drum.
 19. The pumping apparatus of claim 18, wherein each cable guide means is a grooved sheave.
 20. The pumping apparatus of claim 19, and cam means coupled to said shaft, and means responsive to said cam means for controlling the delivery rate of said pump.
 21. The pumping apparatus of claim 17, and hydraulically operated means for rotating said shaft.
 22. The pumping apparatus of claim 16, wherein said control network includes servo loop means for controlling the acceleration of said drum.
 23. The pumping apparatus of claim 16, wherein said control network includes means for stopping the rotation of said drum.
 24. The pumping apparatus of claim 9, wherein said control network includes means for stopping the delivery of hydraulic fluid from said pump to said motor, and means for stopping said prime mover.
 25. In a long-stroke pumping apparatus comprising: a frame, a drum support pivotally mounted on said frame, a drum rotatably mounted on said support, a pair of cable guide means mounted on said frame, traction cable means drivingly coupled to said drum, cable connector means connected to one end of said traction cable means, a counterweight connected to the other end of said traction cable means, reversible power means for rotating said drum, means including a closed servo loop means for controlling the rotation of said drum support simultaneously with and in relation to the rotation of said drum by said reversible power means, the rotation of said drum support being dependent upon the fleet angle of said traction cable means, a sensor means for sensing the instantaneous lateral positions of said traction cable means and for producing a corresponding error signal, said rotation of said drum support being controlled by said error signal produced by said sensor means.
 26. The pumping apparatus of claim 25, and means responsive to said error signal for rotating said drum support in a direction so as to reduce said error signal.
 27. The pumping apparatus of claim 25, wherein said drum support is rotated so as to maintain a substantially zero fleet angle for said traction cable means. 